(CNN) – Republican Rep. Tom Cotton of Arkansas announced Tuesday he will challenge Mark Pryor, the senior senator from his state and one of the most vulnerable Democrats up for re-election next year.

"No one will outwork me in this campaign. I will always defend our shared principles when they are attacked by anyone. I will do the right thing, even when it's the hard thing. And I will never, ever forget how I was raised or where I come from," the freshman congressman told a crowd at his campaign launch in Dardanelle Tuesday.
Cotton has events planned around Arkansas the next few days as he begins courting votes, according to a campaign aide.

Cotton, who served in the wars in Iraq and Afghanistan, is considered a rising star in the GOP and a favorite of many neo-conservatives. The sixth generation Arkansan, who was just elected to Congress this past November, has been a frequent guest on cable news channels, including CNN.

He currently sits on the Financial Services and Foreign Affairs Committees in the House.

With Pryor being one of the few Democratic senators defending his seat in a mostly-red state, the Arkansas contest will be closely watched next fall. Two of the top non-partisan political handicappers, the Cook Political Report and the Rothenberg Political Report, both rate the race as a toss-up. And a pro-GOP poll released Tuesday indicates the contest starts basically tied.

Cotton immediately faces a wide campaign cash gap compared to Pryor. Recent Federal Election Commission reports show the incumbent has a healthy amount of cash, with about $4 million in his campaign war chest. Cotton has just over a million in his congressional campaign, as of June 30.

Pryor is seeking his third term in the Senate. He was first elected in 2002 with 54% and handily won re-election in 2008 with a whopping 80% of the vote.

The senator, 50, has deep political roots in the state. His father, David, served as governor, U.S. senator and U.S. representative. His grandmother, Susie Newton, was the first woman in Arkansas to seek office after women obtained the right to vote and one of the first women to hold a seat on a local school board.

Since elected to the Senate, Pryor has gained a reputation for his mostly centrist voting record and has become known for going toe-to-toe with the Environmental Protection Agency, a government entity with few fans among Republicans.

He also made headlines this year in the gun control debate for being one of four Democrats to join most Republicans in voting against a bipartisan proposal that would have required background checks on firearms purchased online or at gun shows.

He was soon targeted by pro-gun control groups, forcing Pryor to put up a television ad defending his vote.

Preparing for Cotton's bid, Pryor's campaign released a 60-second ad, blasting the recently-elected congressman for "blind ambition" and chasing higher office during his first term in the House.

"Tom Cotton is now running for the Unites States Senate, running for another office just seven months after being sworn into Congress," the ad's narrator says.

The spot hits Cotton for his voting record, including his votes against the Violence Against Women Act and the farm bill. It also attacks the congressman for being one of only 31 members in the House to vote against a bill this summer that would roll back student loan interest rates, despite benefiting from private and Stafford loans himself.

The Harvard graduate explained his vote in a statement released last week, saying taxpayers are "on the hook" for billions in student loan debt.

"Unfortunately, too many students today struggle for years to repay their loans because Washington politicians dictate student-loan rates and end up hurting students and taxpayers alike," he said. "It's causing tuition costs to skyrocket, leaving students buried in debt, often without jobs, and forced to delay buying a home and starting a family."

The National Republican Senatorial Committee, meanwhile, made Pryor's approval of Obamacare a main line of attack.

"In Arkansas, only Senator Mark Pryor and the LSU Tigers are as unpopular as ObamaCare – a law which he was the deciding vote for," NRSC Press Secretary Brook Hougesen said in a statement released Tuesday.

While Pryor voted for the health care bill in December 2009, he joined only two other Democrats a few months later to vote against a reconciliation package that amended the law.

Next year, Democrats will try to maintain their majority in the Senate, where they currently hold a 54-46 edge (including two independents who caucus with the party) over the GOP. They hope to expand that to 55-45 following October's special Senate election in New Jersey, which they are favored to win.

But they most likely will be defending 21 of 35 seats up for grabs in November 2014.

Republicans are optimistic about capturing seats in three states that vote red in presidential elections and have Democratic incumbents retiring: Montana, South Dakota, and West Virginia.

If the GOP captures those three states, it only needs three more seats to reach the magic number of 51 and take control of the Senate.

Republican eyes are focused on four Democrats facing tough battles next year: Pryor, Sen. Mary Landrieu in Louisiana, Sen. Kay Hagan in North Carolina, and Sen. Mark Begich in Alaska.

Take three of those four races and the Republicans will do what they couldn't do in 2010 and 2012: win back the majority.